1. Field of the Invention
The present invention is directed to the field of automotive voltage regulators for use with mechanically driven alternators and more specifically to the area of providing control of the alternator to reduce its output current at elevated temperatures.
2. Description of the Prior Art
Conventionally, vehicles with internal combustion engines employ electrical storage devices (batteries) to provide the energy necessary to start the engine and provide a limited amount of power to energize electrical accessories and lights when the engine is not running.
When the engine is started, electrical power is supplied by an electrical generator, which in recent years has been in the form of an alternator, that supplies a DC voltage sufficient to supply all the electrical requirements of the vehicle and to charge the battery. The alternator output voltage is controlled by a voltage regulator that alternately opens and closes the current path of the alternator field winding in response to the sensed voltage level present at the DC output of the alternator.
The increase in available electrical accessories on vehicles of recent years has dictated increased alternator capacity while at the same time, the smaller sized vehicles have decreased the engine compartment size and have dictated that the alternators be reduced in physical size. In addition, alternators have been recently proposed which physically mount the regulator circuitry on the alternator in order to conserve space and wiring. The increased output capacity, combined with decreased package size and decreased engine compartment size has resulted in alternators which generate more heat and which are less able to dissipate that heat. Of course, high heat is detrimental to the life of an alternator as well as an associated regulator circuitry. Besides obvious mechanical problems, which may occur, there are also numerous electrical components which may be degraded by such an environment. High heat in the alternator may cause junction breakdown of the alternator rectifier diodes. High heat in the regulator environment may cause the field current switching transistors or any other control transistors to fail and possibly cause further alternator damage. Therefore, it is most desirable to keep the alternator from overheating, and some have proposed to provide dedicated fresh air ducts to assist the dissipation.